A switching power circuit having a counter which periodically counts a value between a first value and a second value, a determining unit which continuously determines a third value between the first value and the second value, based on a voltage difference between an output voltage and a reference voltage, a driving unit which alternately switches a first switching element and a second switching element, base on a small and large relation between a counting value of the counter and the third value, and a control unit which resets the counting value of the counter to the first value, based on the voltage difference or a current value at the second switching element.